An EL device is a self-emitting device so that it has a high visibility. Further, it is a complete solid device and therefore has excellent shock resistance. Since an EL device has these features, there have been proposed a variety of inorganic EL devices using an inorganic compound as a light-emitting material and a variety of organic EL devices using an organic compound (this compound will be referred to as "organic light-emitting material" hereinafter) as a light-emitting material, and attempts are being made to use them practically.
Of the above devices, an organic EL device makes it possible to decrease an applied voltage to a great extent as compared with an inorganic EL device, and studies have been and are therefore actively made on the development and improvement of materials for accomplishing an organic EL device having higher performances. The organic EL device is being used as a surface light source, and since devices which emit various colors of light have been developed, it is also being applied to a display unit as a pixel. In a display unit using an organic EL device as a pixel, pixels formed of organic EL devices are two-dimensionally arranged on one plane to form a panel (organic EL display panel), and the organic EL devices (pixels) constituting the organic EL display panel are independently driven to allow the unit to display as desired.
An organic EL device is generally formed on a substrate, and in the basic constitution of an organic EL device of a type using the substrate side as a surface through which light comes out, an anode (transparent electrode) is formed on the substrate and a light-emitting layer and a cathode are consecutively formed. For improving the performance of the device, a hole-injecting layer is provided between the anode and the light-emitting layer and an electron-injecting layer is provided between the cathode and the light-emitting layer in some cases.
The material for the above transparent electrode (anode) is selected from transparent electrode materials having a surface resistance of about 15 .OMEGA./.quadrature. or more such as crystalline ITO, ZnO:Al and the like. When the transparent electrode formed of the above material is used to produce, e.g., a X-Y matrix type organic EL display panel, the transparent electrode is required to have a relatively large thickness, as large as approximately 200 nm or more, and the electric resistance of the transparent electrode line is required to be approximately 10 K.OMEGA. or less, for preventing a decrease in display performances caused by a voltage drop, an increase in consumption power and an increase in RC time constant.
However, the use of the above thick transparent electrode (transparent electrode line) causes problems that (a) the device causes a short circuit due to a height-level difference of edge of the transparent electrode (height-level difference between upper surface of transparent electrode and surface of substrate), and that (b) an organic single-layer portion or an organic multi-layer portion, or an opposing electrode laminated on the organic single-layer portion or on the organic multi-layer portion, suffers the breakage of a line (the breakage of a line will be referred to as "height-level-difference-induced breakage" hereinafter) to cause a point defect or a line defect on an image.
Further, when the thickness of the transparent electrode is increased up to approximately 200 nm or more in the transparent electrode formed of the above transparent electrode material, the flatness of the transparent electrode surface is impaired. When an organic single-layer portion or an organic multi-layer portion and an opposing electrode are laminated on the above transparent electrode to obtain an organic EL device, there are caused problems that (c) a local concavo-convex shape increases so that a high voltage is locally caused during its driving, which results in a non-uniformity in brightness and consequently accelerated deterioration of the device, so that the stability in light emission is decreased, and that (d) the crystallization of an organic compound forming the organic single-layer portion or the organic multi-layer portion is accelerated, which results in a non-uniformity in brightness and a decrease in light emission capability.
As a method of preventing the height-level-difference-induced breakage caused on other layer when the other layer is formed on the transparent electrode, there is known a method, which is a method in an inorganic EL device, in which a plurality of stripe-shaped insulation films or glass protrusions are formed on a glass substrate and a transparent electrode having nearly the same height as that of the insulation films or the glass protrusions is formed between these insulation films or the glass protrusions (JP-A-61-176011).
On the other hand, as a method of preventing the crystallization of an organic compound forming the organic single-layer portion or the organic multi-layer portion in the organic EL device, there is known a method in which the surface of a transparent electrically conductive film which is formed first is polished until its flatness (10-point average roughness) becomes 1/10 to 1/100 of the thickness of a light-emitting layer (organic single-layer portion or organic multi-layer portion) and then patterned into a transparent electrode having a predetermined form (JP-A-4-87187). In this method, however, the fabrication of the transparent electrode, consequently, the production of an organic EL device, is complicated.
The occurrence of the above-described problems (a) to (d) can be prevented to some extent by employing a three-layer-structured thin transparent electrode disclosed in JP-A-2-253593, i.e., a thin transparent electrode in which the order of laminated layers viewed from the substrate side is a transparent electrically conductive layer (metal oxide layer), a thin metal layer and a transparent electrically conductive layer (metal oxide layer). A transparent electrode having a similar layer constitution is also described in European Laid-open Patent Publication No. 736913, column 10, lines 25 to 44.
Further, the occurrence of the above problems (a) to (d) can be also prevented to some extent by a transparent electrode (anode) described in JP-A-6-5369, i.e., an electrode of two-layer structure in which a first anode portion formed of a transparent electrically conductive layer and a second anode portion formed of a thin metal layer having a higher work function than the first anode portion are consecutively laminated when viewed from the substrate side and the first anode portion has a small thickness.
However, even if the above small-thickness transparent electrode having the above structure of a plurality of layers is used, the above-described problems (a) to (d), (a) and (b) in particular, are liable to occur when it is required to form a number of organic EL devices like an organic EL display panel.